Blackhead disease, invariably fatal, occurs in birds of all ages. Its economic impact in terms of losses is greatest in turkeys, which are particularly susceptible to the disease. Other poultry and birds, e.g., chickens, guineas, quails, pheasants and pea-fowl, also frequently contract the disease which is caused by a flagellate protozoan identified as Histomonas meleagridis. Its clinical symptoms are manifested by lesions and inflammation of the ceca and liver. Because of its etiology and gross pathology, the disease is known as histomoniasis and/or infectious enterohepatitis.
Histomonas meleagridis is mostly harbored by the common poultry cecal worms, Heterakis gallinarum, and its eggs, in which it is able to live for extended periods. This source is mainly responsible for the transmission of the disease.
The disease is contracted orally by the birds when consuming feed or water contaminated with droppings containing the infectious organism or by swallowing cecal worms or their eggs harboring the parasite. The incubation period of blackhead is about 14 to 21 days. The disease manifests itself in the infected birds by inappetence, a constant yellowish or sulfur colored diarrhea and weight loss followed by death. Generally, yound birds are more susceptible than adults, although the mortality rate in both groups is very high. Adult birds are usually sick for several days losing much weight before they die while the yound birds succumb much quicker.
Post-mortem examinations of the birds disclose multiple lesions and ulcerations of the cecal wall and liver. The ceca are filled with yellowish-green cores and the cecal walls are thickened. The lesions of the liver consist of large irregular reddened or gray necrotic areas.
In turkeys particularly, the prognosis of the disease is poor. The high mortality rate, at times 100% of the flock, results in large losses to the poultry breeder. Losses are in excess of $4 million annually. Heaviest losses are during the first three months of life, however, other age groups are also affected. The disease is prevalent in all areas where turkeys are raised.
The prevention and control of blackhead disease is at present effected by various chemotherapeutic agents such as arsenicals, nitrothiazoles, nitrofurans and nitroimidazoles.
This invention provides histomonostat compositions containing certain 2-carbalkoxy-amino-benzimidazole-5(6)-phenyl esters for combatting blackhead disease by preventing and curing the disease and which not only possess a high degree of efficacy with negligible side effects at low dosages but also do not suppress the weight gain of the treated infected birds.